LOCAL STRUCTURE AND NANOSCALE PROPERTIES PHYSICOCHEMISTRY OF LIQUIDS, The Pu L edge XANES spectra acquired for a selection of HC and SC SOFT MATTER, NANOCHEMISTRY samples evidenced the strong predominance of the (+IV) oxidation state3 SYNCHROTRON SOLEIL HIGHLIGHTS 2020 for the Pu. Their EXAFS spectra were compared with “bulk” PuO and a2 cluster of Pu(IV) used as references. Besides the observation of two main peaks located at R-φ= 1.84 and 3.68 Å agreeing with the k-weighted3 MARS BEAMLINE FT spectra of bulk PuO, EXAFS analyses reveal two distinctive features2 for both colloid samples: i) a reduced amplitude for both Pu-O and Pu- Associated publication Pu coordination shells, and ii) a strong asymmetry and distortion of the Relevance of formation conditions Pu-O coordination sphere (Fig. 2). Both effects appear correlated to on the size, morphology and local the NP size shrinking probed by SAXS as evidenced by their spectra structure of intrinsic plutonium colloids. observed to be framed with the references. Data fitting demonstrates the dependency of the local structural disorder with the NP size for the C. Micheau, M. Virot, S. Dourdain, Pu-O shell fitting. Such phenomenon is explained by a surface effect T. Dumas, D. Menut, P. L. Solari, resulting from the increasing proportion of Pu atoms standing at the L. Venault, O. Diat, P. Moisy, surface of a NP when shrinking.[3,4] The distortion of the Pu-O sphere S. I. Nikitenko. can be explained by the contribution of other surface moieties (ex: µ-1 Environmental Science: Nano., Pu-OH, µ-Pu-O, Pu-HO) which hypothesis is confirmed by the EXAFS3 2 7, 2252 (2020). simulation of Pu38 cluster (Fig. 2).[5] FIGURE 2 References [1] C. Walther & M. A. Denecke, Chemical Reviews, 113, 995 (2013). [2] E. Dalodiere et al., Scientific Reports, 7:43514 (2017). [3] L. Bonato et al., Nanoscale Advances, 2, 214 (2020). [4] A. Kuzmin & J. Chaboy, IUCrJ, 1, 571 (2014). [5] L. Soderholm et al., Angewandte Chemie-International Edition, 47, 298 (2008). Corresponding author Matthieu Virot Institut de Chimie Séparative de Marcoule ICSM UMR 5257 UM/CEA/CNRS/ ENSCM Laboratoire de Sonochimie dans les Fluides Complexes (LSFC) Site de Marcoule, Bâtiment 426 BP 17171 MEETING SAXS VS. XAS RESULTS 30207 Bagnols sur Cèze Cedex, France matthieu.virot@cea.fr The results obtained by both SAXS and XAS approaches converge in the description of the highly debated Pu(IV) intrinsic colloids as core-shell Captions NPs made up of a PuO core covered with a size-dependent disordered2 FIGURE 1: SAXS diagrams acquired on SC and HC Pu-O shell. The strong influence of the preparation method on the intrinsic colloids. Black lines indicate the slope power multi-scale properties of Pu(IV) intrinsic colloids is demonstrated. The laws. local structure of both coordination spheres (XAS) appears correlated The inset shows the X-Ray scattering length density with the NP shrinking (SAXS) rather from the contribution of unusual profile of HC obtained from the simulations of the core- shell model. features. The stabilization of the HC particles is further suggested with 2: Fourier transforms (FT) of the k-weighted FIGURE 3 SAXS simulation to result from the interaction with counter-ions from 2.5-15 Å interval for a selection of HC and SC compared1 the medium. The new insights reached about the local structure, size, with bulk PuO2 and simulated Pu38 cluster used as morphology and interfacial properties of intrinsic Pu(IV) colloids could help references. in a better understanding of Pu migration mechanism in the environment and pave the way for original investigations with radioactive materials. 35